Field of the Invention
The present invention relates to a sensor-equipped wheel support bearing assembly in which an incorporated load sensor unit is operable to detect a load acting on a bearing structure that supports a wheel.
Description of Related Art
In order to determine a load acting on a wheel of an automotive vehicle, a wheel support bearing assembly has been proposed, which includes a strain gauge affixed on an outer ring of the bearing assembly to sense strain in an outer diameter surface of the outer ring, so that a load can be determined based on the sensed strain (see, the Patent Document 1 listed below). Such a technique disclosed in the Patent Document 1, however, may not allow for accurate determination of a load acting on a wheel support bearing assembly, because the deformation of a stationary member (i.e. strain in the stationary member) that occurs in response to the load may be inadequate. Hence, the detection sensitivity may be unsatisfactory.
In the attempt to remedy this inadequacy, a sensor-equipped wheel support bearing assembly of the following configuration or construction has been proposed (see, the Patent Document 2 listed below). The Patent Document 2 discloses a sensor-equipped wheel support bearing assembly which includes an outer member having an inner periphery formed with double row rolling surfaces, an inner member having an outer periphery formed with rolling surfaces held in face-to-face relation with the previously described rolling surfaces, and double row rolling elements interposed between the respective rolling surfaces in the outer and inner members and is operable to rotatably support a vehicle wheel relative to a vehicle body structure. One of the outer and inner members, which defines a stationary member, has an outer diametric surface provided with at least one sensor unit pair, each pair being made up of two sensor units arranged at positions that are spaced from each other in a direction circumferentially of the stationary member a distance enough to have a 180° phase difference therebetween. Each sensor unit is made up of a strain generating member, which has at least two contact fixing segments fixed in contact with the outer diametric surface of the stationary member and a sensor fitted to the strain generating member for detecting a strain occurring in the strain generating member.
According to this configuration or construction, a radial load estimating section estimates a radial load acting in a direction radially of the bearing unit from a difference between respective output signals of the two sensor units of the sensor unit pair. And an axial load estimating section estimates an axial load acting in a direction axially of the bearing unit from the sum of those output signals of the two sensor units of the sensor unit pair. The at least one sensor unit pair may include two sensor units that are arranged on upper and lower surface areas of the outer diametric surface of the stationary member, which correspond respectively to top and bottom positions relative to a tire tread surface or a tire periphery in contact with a road surface. An axial load direction determining section may determine a direction of the axial load, from amplitudes of the respective output signals of the sensors of the at least one sensor unit pair. FIG. 20 is a block diagram that schematically shows a load estimation operation according to this configuration or construction.
Such a sensor unit may be arranged so that the contact fixing segments of the strain generating member thereof are in the vicinity of a rolling surface of a stationary member of the wheel support bearing assembly. In this case, rotation of a wheel can induce a sinusoidal-like variation, such as shown in FIG. 21, in output signals of sensors. This variation is caused by the change in sensed strain, which is attributable to the passing-by of rolling elements. In this configuration or construction, the difference in amplitude (i.e. difference in amplitude of a frequency component attributable to revolution of rolling elements) between sensor output signals of two sensor units that may be positioned upwardly and downwardly, respectively, may be used to determine an axial load. The axial load may be calculated using appropriate load estimation parameters, which are selected according to whether the determined direction of the axial load is negative or positive. In this way, a load may be estimated with good sensitivity.
Such a configuration as disclosed in the Patent Document 2, however, requires an amplitude value of sensor output signals to be calculated, to enable selection of optimal load estimation parameters. Hence, such a configuration is disadvantageous when an amplitude value cannot be obtained. Specifically, when a wheel is not rotating or when the wheel rotation speed is very low, change in signals in response to application of a load to rolling elements is either zero or occurs very slowly. In such a case, change in sensor output signals cannot be used to calculate an amplitude value.
Nevertheless, in order to obtain an amplitude value of sensor output signals in response to application of a load to rolling elements, it may be contemplated to arrange a plurality of sensors so as to cover a range (i.e. a circumferential length corresponding to arrangement pitch of the rolling elements) sufficient to monitor the influence of the load applied to the rolling elements. In this way, direct measurement of strain distribution may be obtained. However, this requires an additional number of sensors and results in more complicated circuit structure for detection, thereby leading to higher cost and increased burdens for ensuring reliability.
In view of the foregoing, a load estimating section for a sensor-equipped wheel support bearing assembly, which has a configuration as shown in a block diagram of FIG. 22, has been developed (see the Patent Document 3 listed below).
Such a configuration includes a first load estimating section for calculating and estimating a load, acting on the wheel support bearing assembly, using an average value of output signals of sensors, a second load estimating section for calculating and estimating a load, acting on the wheel support bearing assembly, using the average value and an amplitude value of output signals of the sensors, and an output selector for selectively switching one of the loads estimated by the first and second load estimating sections in dependence on a vehicle wheel rotating speed.
In such a configuration, load estimating calculation may be switched in dependence on a vehicle wheel rotating speed between a load estimating calculation equation that uses as a variable an average value A of output signals of the sensors and a load estimating calculation equation that uses as variables the average value A and an amplitude value B of output signals of the sensors. Hence, in normal travel regime, an equation that uses an average value A of output signals of sensors and an amplitude value B of output signals of the sensors may be utilized in load estimating calculation, while, in low speed regime or when a wheel is not rotating, an equation that uses the average value A of the output signals of the sensors may be utilized in load estimating calculation. Note that, in such a configuration, information related to a vehicle wheel rotating speed may be used to determine the rotating speed.